The present invention relates to an improved package adapted to be used for packaging popcorn and more particularly to an expandable disposable package for popping popcorn in a microwave oven.
Popcorn has been heated in microwave ovens by coating the kernels with oil or butter and then enclosing the popcorn kernels within a paper or plastic bag. The microwave oven is turned on and the oil and kernels absorb microwave energy. The kernels then become hot and expand until they pop. A drawback to this method is that oil has been found to make the popped kernels greasy, less appealing and possibly pose a health risk. Further, it has been found that butter can become rancid after a period of time as might occur when the packages are stored on shelves for a lengthy period.
Another food package for cooking popcorn in a microwave oven is disclosed in U.S. Pat. No. 4,586,649. This package uses the technique known as "clumping" to concentrate the corn kernels in a small, compact area by having the configuration of the package be such that kernels be held together in an area or region of high heat concentration. As the kernels are heated, they will pop. When they pop, the heavier and smaller unpopped kernels will tend to fall back in to the area of greatest heat concentration during the popping process. This clumping technique is also described in U.S. Pat. No. 4,158,760. Using this method, an expandable bag of plastic film contains unpopped kernels and is located within a carton. The walls of the carton are shaped such that when the kernels pop, the unpopped kernels remain in a cluster or clump around the bottom of the carton. As the popcorn is heated, the top of the carton and the bag expands upward. One drawback of this package is that because of the shape of the package, the carton may take up significant shelf space on a store shelf. Further, this package, when used as a disposable carton, uses a plastic bag, which may interfere with the clumping process.
Another technique used for popping corn is placing the kernels in a container having a floor constructed from a microwave absorbing material, such as ferrite or waterglass coated over a thick metal sheet or ceramic. The microwave energy causes the floor to become hot and heat the kernels by conduction. Kernels contain a small amount of moisture which turns into steam when heated. When the kernels become hot, they expand or explode from the build up of pressure from the steam (internal temperature of explosion is approximately 420.degree. F.). This method has a drawback in that ferrite material is not readily adaptable for disposable microwave packaging, as the ferrite becomes extremely hot and may burn paper it contacts. Another drawback is that the material used on the floor must be heated for a long period of time before it becomes warm. Further, the material used on the floor remains hot for a significant period of time after heating. Hence, the floor must be allowed to cool before it can be touched.
Heating popcorn in a disposable package in a microwave oven with the previously described techniques has the drawback that the popcorn can only be left in the oven for a short period of time once the first kernel pops. If the kernels are allowed to remain in the oven longer than that short time, the popped kernels will start to scorch and degrade. These techniques further require a long amount of time to pop all the kernels. Consequently, a large amount of kernels will not become popped.